A ball bearing assembly process includes a ball arranging process of inserting balls into a gap space between an outer ring and an inner ring and then arranging the inserted balls at equally spaced intervals. As the ball arranging process, four following methods may be exemplified, for example.
(1) Manual: The balls are moved by using a bamboo skewer or the like. Since the ball is positioned with eyes, it is difficult to correctly distribute the balls at equally spaced intervals.
(2) Ball distribution arrow: As disclosed in Patent Document 1, the balls are arranged at equally spaced intervals by inserting a comb-shaped ball distribution jig, which has a plurality of operation arrows having different axial lengths and protruding along a ball pitch circle of a ball bearing, into a gap area between the inner and outer rings. First of all, a ball gathering operation of gathering the plurality of balls to one area in a circumferential direction should be performed. Also, when the number of balls increases, it is necessary to lengthen an axial length of a ball distribution arrow 111 as shown in FIG. 16. In this case, the ball distribution arrow is difficult to be manufactured and is expensive.
(3) Air ball distribution: As disclosed in Patent Document 2, the balls are arranged at equally spaced intervals by air injection and suction. The ball gathering is not required. However, an expensive nozzle for air injection and suction is required.
(4) Magnetic ball distribution: As disclosed in Patent Document 3, the balls are arranged at equally spaced intervals by bringing a magnet close to a raceway surface space between the inner and outer rings to apply a magnetic field to the raceway surface space and thus generating magnetic repulsive forces between the respective adjacent balls. The ball gathering is not required but a strong magnet is required.
Among the above methods, the air ball distribution and the magnetic ball distribution are not generally used because the expensive dedicated jig and tool are required. At present, the ball distribution arrow method is adopted as an automatic ball distribution method which is relatively inexpensive and is suitable for the mass production.